The goals of this project are to develop and test improved viral vector systems for gene transfer to striated muscle. A particular focus is on the ability to transfer genes to muscles of adult and old mice, with an emphasis on models for Duchenne muscular dystrophy (DMD). DMD is among the most common human genetic diseases, and represents the most common genetic disease affecting skeletal muscle. Two vector systems will be explored: gutted adenoviral (Ad) and adeno-associated viral (AAV) vectors. Both of these systems have significant potential for use in gene transfer, but they each require additional development to enable clinical use in a safe and efficacious manner. Technological improvements to these vectors systems will therefore constitute a major component of the project goals. A second component of the project will explore the use of these vector technologies to modify muscles of adult and old animals, with a goal of correcting functional deficits that progressively increase with aging in both normal and dystrophic muscles. We will develop improved packaging cell lines, vectors and helper viruses to increase the yield, purity and ease of preparation of gutted Ad vectors. We will also explore the use of AAV serotype 6 for gene transfer to muscle. AAV serotype 6 displays highly efficient gene transfer to muscle, and we propose to optimize methods to obtain high titer stocks of highly purified AAV6 vectors displaying muscle-specific expression. Both types of vectors will be used to characterize the ability to prevent, halt or correct features of muscular dystrophy in the mdx mouse model of DMD by delivery of full-length, mini or micro-dystrophins. Studies will be conducted in young, adult and old mice, and will explore potential immunological consequences of delivery of these vectors to striated muscle. Finally, we will use these systems to explore additional phenotypic features of dystrophy in aging mice, with a goal of developing methods to arrest, and at least partially reverse, functional deficits of striated muscles by gene delivery of dystrophin and Igf-1. Studies that lead to improved methods for gene delivery and the amelioration of abnormalities of dystrophic muscles in adult and old animals will not only facilitate development of a treatment for DMD, but can also serve as a model for the development of genetic therapies for other genetic diseases and conditions associated with aging.